A variable valve device for an internal combustion engine transmits a turning force from a main drive shaft (a crankshaft) of the internal combustion engine to a camshaft via a timing chain and a timing belt, and rotates cams provided on the camshaft, thereby causing the cams to act on intake and exhaust valves (valves) to open/close the valves.
In recent years, there have been known variable valve mechanisms that are designed to change the working angle of a valve by changing the period in which a cam acts on the valve. Patent Document 1 discloses a variable valve system for an internal combustion engine that changes the lift amount of a valve with respect to a rotational position of a cam and changes the working angle of the valve by rotating a control shaft that is interposed between the cam and the valve, with the aid of a drive source. Patent Document 2 discloses a variable valve device that changes the working angle of a valve by interposing an annular disc between a flange portion of a sleeve coupled to a drive shaft and a flange portion of a camshaft, and making the center of the annular disc eccentric to cause the annular disc to rotate at non-constant speed.